This invention relates to a copper-nickel catalyst containing on an inert, refractory carrier metallic copper and nickel as active component bound to the carrier. The invention also relates to a process for producing that catalyst and to its use, in particular for the methanation reaction, in which carbon monoxide and hydrogen are reacted to form methane.
Copper-nickel catalysts containing metallic copper and nickel as the active component on an inert, refractory carrier are known, for example for DE-A-20 25 501, US- Pat. Nos. 4,157,315, 3,371, 050 and 3 956 191.
In the DE-A-20 25 501 copper-nickel catalysts are mentioned, where the nickel has a specific function in realizing thermostable copper catalysts. In this disclosure it is stated that thermostable copper catalysts cannot be produced by hitherto known methods, because of the weak interaction betweent the copper and the silica surface. Therefore, a method is proposed in which nickelhydrosilicate particles are formed onto the silica surface. An oxidic copper compound is then precipitated over the nickel compound particles. After reduction the copper particles are well-bounded to the carrier via the intermeidate layer of nickel-metal-nickel-silicate compounds. The nickel will thus not be active as nickel metal, because it is always covered by copper. Consequently these catalysts are only useful for their specific activity as copper catalysts, not as nickel or nickel-copper catalysts. Furthermore, because of the two-layer approach, it will be difficult to produce really small active metal particles. Average particles sizes of 17 and 200 Angstrom are mentioned (=17 and 20 nm respectively).
According to US. Pat. No. 4,157 315, a catalyst containing several metals, for example nickel and copper, as active component is produced by coating a substrate with a dispersion containing a stabilized solution of colloidal silicon dioxide and fine metal powders of the metals forming the active component, heating ths substrate thus coated in an inert gas atmosphere and sintering it at elevated temperature. A coating having low specific surface with low catalytic activity is obtained.
According to U.S. Pat. No. 3,371,050, nickel-copper catalysts can be produced by depositing insoluble compounds together onto the support from a solution of nickel salts and copper salts, separating off, calcining and reducing the loaded carrier. The catalysts thus obtained, in which the nickel content exceeds the copper content, have a small surface of active metals.
According to U.S. Pat. No. 3,956,191, nickel-copper catalysts are produced similarly to the disclosure of DE-A-20 25 501 by depositing an insoluble copper compound from a solution containing copper ions onto a carrier loaded with nickel and separating off, calcining and reducing the loaded carrier. Complete reduction of the nickel is not required and is extremely difficult. In addition, the catalysts described in this literature reference contain approximately twice as much nickel as copper.
The production of catalysts of the type in question is based on the general idea that, on the one hand, pure nickel catalysts tend to deposit carbon when exposed to an atmosphere containing CO or hydrocarbons, whereas on the other hand copper catalysts containing the active metals on an inert, refractory carrier are inactive for that reaction, but on the other hand do not show any tendency to deposit carbon. Accordingly, there is a need for copper-nickel catalysts which are suitable for the above-mentioned methanation reaction and other reactions, in which carbon monoxide and/or hydrocarbons are present in the reaction gas phase (as starting materials or end products) or are intermediately formed, and which catalyze those reactions, but which on the other hand do not show any tendency to deposit carbon.
The copper-nickel catalysts known from the prior art, which contain metallic copper and nickel as active component on an inert refractory carrier, show very poor catalytic activity for the above-mentioned reactions when the nickel content is low. On the other hand, if the nickel content is high, these catalysts present almost the same problems as pure nickel catalysts. The object of the present invention is to provide a copper-nickel catalyst which shows high catalytic activity for the methanation reaction and other reactions of the type described above, for example the low temperature reforming reaction, but which only deposits carbon after prolonged use, if at all. In addition, it would be of advantage if the catalysts in question did not show any tendency to form nickel carbonyls under operating conditions in chemical conversion processes.
It has now been found that this problem can be solved to a considerable degree by the catalyst defined hereinafter.